Magnetic impedance element having at least two thin film-magnetic cores

ABSTRACT

A magnetic impedance element including a substrate made of a non-magnetic material, a thin-film magnetic core formed on said substrate, and first and second electrodes disposed on both ends of said thin-film magnetic core in a longitudinal direction thereof, characterized in that said thin-film magnetic core is formed by laminating a plurality of magnetic films through non-magnetic thin-films.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic-sensor, and moreparticularly to a magnetic impedance sensor which is a high-sensitivemagnetic sensor.

2. Description of the Related Art

As information devices and measuring and control devices are beingrapidly developed in recent years, demand of magnetic sensors which arelow in size and costs and high in sensitivity and response speed haveincreased more and more. For example, in a hard disc device of anexternal memory device for a computer, a high performance has beenadvanced such that an induction type magnetic head of the bulk type hasbeen changed to a thin-film magnetic head or a magnetic resistanceeffect (MR) head. Since in a rotary encoder which is a rotary sensor foruse in a motor, a magnetic ring having a high magnetic density has beendemanded, there has been required a magnetic sensor which is capable ofdetecting a fine surface magnetic flux with a high sensitivity insteadof the conventional magnetic resistance effect (MR) sensor used. Also,demand of high-sensitive sensor which can be used for a non-destructiveinvestigation or a bill investigation has increased more and more.

As representative magnetic detecting elements which are now being used,there are an induction type reproduction magnetic head, a magneticresistance effect (MR) element, a flax gate sensor, a hall element andso on. Also, in recent years, there have been proposed magnetic sensorshigh in sensitivity using the magnetic impedance effect of an amorphouswire (refer to Japanese Patent Laid-open Publication No. Hei 6-176930,Japanese Patent Laid-open Publication No. Hei 7-181239, Japanese PatentLaid-open Publication No. Hei 7-333305) or the magnetic impedance effectof a magnetic thin-film (refer to Japanese Patent Laid-open PublicationNo. Hei 8-75835, Japanese Applied Magnetic Institute Journal, vol.20,553 (1996)).

The induction type reproduction magnetic head suffers from such problemsthat a magnetic head per se becomes large-sized because a coil windingis required, to the contrary, that the sensitivity of detection isremarkably deteriorated in case the number of turns of coil is reducedfor the purpose of making the magnetic head small. On the other hand,the magnetic resistance effect (MR) element using a ferromagnetic filmis being employed. The MR element is so designed as to detect not atemporal variation in magnetic flux but the magnetic flux per se, tothereby advance the miniaturizing of the magnetic head. However, even inthe existing MR element, for example, the MR element using a spin valveelement, the rate of change in the electric resistance is small to thedegree of 6% or less at the maximum, and the external magnetic fieldnecessary for obtaining the resistance change of several % is large tothe degree of 1.6 kA/m or more. Therefore, the magnetic resistancesensitivity is low to the degree of 0.001%/(A/m) or less. Also, inrecent years, there has been found a giant magnetic resistance effect(GMR) due to an artificial lattice in which the rate of change in themagnetic resistance is several tens %. However, in order to obtain theresistance change of several tens %, the external magnetic field ofseveral tens A/m is necessary, and therefore the practical use of themagnetic resistance element as a magnetic sensor has not been realized.

The flux gate sensor which is the conventional high-sensitivity magneticsensor is so designed as to measure the magnetism by using thephenomenon in which the symmetric B-H characteristic of a highpermeability magnetic core such as a permalloy is changed according tothe external magnetic field, and has the high resolution and the highdirectivity of 1. However, the above flux gate sensor suffers from suchproblems that a large-sized magnetic core is required in order toenhance the sensitivity of detection, that it is difficult to reduce thedimensions of the entire sensor and that the power consumption is large.

The magnetic sensor using a hall element is a sensor using a phenomenonin which when a magnetic field is applied perpendicularly to a surfaceof the sensor into which a current flows, an electric field is developedin a direction perpendicular to both of the current flowing directionand the magnetic field applying direction, to thereby induce anelectromotive force in the hall element. The hall element isadvantageous in the costs but has such defects that the sensitivity ofthe magnetic field detection is low and that the temperaturecharacteristic of the magnetic field sensitivity is low because themobility of electrons or positive holes is changed by diffusion oflattices within the semiconductor due to thermal vibrations to a changeof temperature since the hall element is made of semiconductor such asSi or GaAs.

Japanese Patent Laid-open Publication No. Hei 6-176930, Japanese PatentLaid-open Publication No. Hei 7-181239 and Japanese Patent Laid-openPublication No. Hei 7-333305 have proposed therein magnetic impedanceelements by which a great improvement in the magnetic field sensitivityhas been realized. The magnetic impedance element is a magneticimpedance element that has a basic principle in which only a voltagecaused when a circumferential magnetic flux changes as a time elapses,which is produced when a current which varies as a time elapses issupplied to a magnetic line is detected as a change caused by theexternally applied magnetic field. FIG. 16 shows an example of themagnetic impedance element. In the magnetic impedance element 1 of FIG.16, an amorphous wire (a wire which has been tension-annealed afterhaving been drawn) which is made of FeCoSiB or the like and about 30 μmin the diameter of exciting distortion is employed as a magnetic line 2.FIG. 17 is a graph showing the applied magnetic field dependency of thewire (for example, the magnetic line 2 in FIG. 16) with respect to theimpedance change. Even in a wire having a small dimension of about 1 mmin length, when a high-frequency current of about 1 MHz is supplied tothe wire, the amplitude of a voltage across the wire changes with thehigh sensitivity of about 0.1% /(A/m) which is 100 times or more of theMR element.

As the magnetic sensor, there has been demanded a high-sensitivemagnetic sensor which is small in size, low in the costs and excellentin the linearity and the temperature characteristic of an output to thedetected magnetic field. The magnetic sensor using the magneticimpedance effect of the amorphous wire exhibits the magnetic fielddetection characteristic of a high sensitivity. Also, Japanese PatentLaid-open Publication No. Hei 6-176930 and Japanese Patent Laid-openPublication No. Hei 6-347489 disclose that the application of a biasmagnetic field allows the linearity of the dependency of the appliedmagnetic field on the impedance change to be improved; and that anegative feedback coil is wound on the amorphous wire, and a currentproportional to a voltage between both ends of the amorphous wire issupplied to the coil to conduct negative feedback, thereby being capableof providing a sensor (high-sensitive magnetic impedance element) whichis excellent in linearity and uniform in the magnetic field detectionsensitivity with respect to the temperature change of the sensorsection.

However, because the high-sensitive magnetic impedance element is formedof the amorphous wire the diameter of which is about 30 μm, it is notproper for fine machining, thereby making it difficult to provide asuper-miniaturized magnetic detecting element. Also, since both of thebias coil and the negative feedback coil must be prepared by winding athin copper wire, there is a limit of miniaturizing the high-sensitivemagnetic impedance element, and there also arises a problem from theviewpoint of productivity such that the soldering property of theelectrode is low since an oxide film is formed on the surface of thewire.

In addition, if the length of the element is lengthened in order toincrease the impedance of the element for the purpose of obtaining alarge sensor output, it is not proper for the miniaturization of themagnetic sensor. On the other hand, there is proposed that the wire isbent in a zigzag manner for use. However, in this case, since the wiremade of a magnetic material is bent, the magnetic characteristic isdeteriorated by a strain stress with the result that a sensor output isremarkably degraded. Also, there is proposed that a wire is divided intoa plurality of pieces, the divided wires are disposed in parallel andelectrically connected in series. However, in this case, there arises aproblem of productivity such as a problem of electrode soldering.

On the other hand, as an attempt to miniaturize the magnetic impedanceelement, there has been proposed a magnetic impedance element using amagnetic thin-film in Japanese Patent Laid-open Publication No. Hei8-75835, by which the element is going to be miniaturized. Also, thepresent inventors have proposed a miniaturized magnetic impedanceelement in which a thin-film coil is wound around a thin-film magneticcore three-dimensionally to provide a bias coil and a negative feedbackcoil in Japanese Patent Application No. Hei 9-269084. However, themagnetic film of those proposed elements is of a single-layer structure.

In this case, if the variation amount ΔZ/Z of the impedance and thewidth and the thickness of the element are kept constant in order totake a large sensor output, that is, in order to take a large variationamount ΔZ of the impedance, the length of the element must belengthened. For that reason, there arises such a problem that the entirechip size becomes large.

Although the details will be described with reference to embodiments ofthe present invention, a magnetic domain structure shown in FIG. 3A isideal, and in fact, when a uniaxial anisotropy is given in the widthwisedirection of a single-layer thin-film pattern, a diamagnetic field isdeveloped in the widthwise direction, and in order to minimize thediamagnetic energy, the magnetic domain structure becomes a state wherethe magnetic vector is closed as shown in FIG. 5. However, when themagnetization vector is directed to the longitudinal direction of thethin-film pattern, since a magnetic permeability μθ in the widthwisedirection due to the external magnetic field Hex is hardly changed, theMI effect becomes very small. In other words, the MI effect of the 90°magnetic domain portion shown in FIG. 5 is very small so that the MIeffect of the entire thin-film becomes small.

Also, as shown in FIG. 3 on pages 66 to 69 of “Electronic Technology”(Nikkan Kogyo Shinbunsha) 1992-December, there has been proposed amagnetic impedance (MI) element in which the length of a magnetic coreis lengthened by bending a magnetic thin-film in a zigzag manner.However, in this structure, a magnetic domain structure at curvedportions is complicated, and when a magnetic field is applied to themagnetic impedance element from the external, the magnetic walls of thecurved portions cause noises due to a rapid change of the output voltagefrom the element which is caused by Barkhausen jump which ununiformlymoves.

Further, there has been proposed a magnetic sensor which is structuredsuch that a pair of magnetic detecting sections each of which is made upof an amorphous wire and a coil for applying a bias magnetic field tothe wire are disposed in parallel to conduct differential drive, therebyimproving the sensitivity, in Japanese Patent Laid-open Publication No.Hei 7-248365.

However, because the high-sensitive magnetic impedance element is formedof the amorphous wire which is about 30 μm in diameter, it is not properfor fine machining, as a result of which it is difficult to provide asuper-miniaturized magnetic detecting element. Also, since both of abias coil and a negative feedback coil must be prepared by winding athin copper wire, there is a limit of miniaturizing the high-sensitivemagnetic impedance element and there also arises a problem from theviewpoint of productivity such that the soldering property of theelectrode is low since an oxide film is formed on the surface of thewire. In particular, as disclosed in Japanese Patent Laid-openPublication No. Hei 7-248365, in case of the differential drive, becausetwo magnetic detecting elements are employed, the miniaturizing of themagnetic impedance element becomes increasingly difficult, and theproductivity is also deteriorated. In addition, because the bias coiland the negative feedback coil must be wound around the respectiveamorphous wires, an interval between two wires requires a space forwinding the coil, and the distance between those wires becomes long asmuch, thereby making it difficult to accurately detect a small localmagnetic field.

On the other hand, as an attempt to miniaturize the magnetic impedanceelement, there has been proposed a magnetic impedance element using amagnetic thin-film in Japanese Patent Laid-open Publication No. Hei8-75835, by which the element is going to be miniaturized. Also, thepresent inventors have proposed a miniaturized magnetic impedanceelement in which a thin-film coil is wound around a thin-film magneticcore three-dimensionally to provide a bias coil and a negative feedbackcoil in Japanese Patent Application No. Hei 9-269084. However, even inthose inventions, two chips must be used in order to employ thoseinventions in a differential drive circuit. For that reason, because aninterval between two thin-film magnetic cores becomes long, it isdifficult to accurately detect a small local magnetic field similarly asin the Amorphous wire.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances,and therefore an object of the present invention is to provide ahigh-sensitive magnetic sensor element which is small in size, low inthe costs, high in output and excellent in the linearity and thetemperature characteristic of an output detecting magnetic field withthe above magnetic sensor

In order to achieve the above object of the present invention, accordingto a first aspect of the present invention, there is provided a magneticimpedance element including a substrate made of a non-magnetic material,a thin-film magnetic core formed on said substrate, and first and secondelectrodes disposed on both ends of said thin-film magnetic core in alongitudinal direction thereof, characterized in that said thin-filmmagnetic core is formed by laminating a plurality of magnetic filmsthrough non-magnetic thin-films.

According to a second aspect of the present invention, there is provideda magnetic impedance element as defined in the first aspect of thepresent invention, characterized in that the thin-film magnetic core isformed by laminating the plurality of magnetic films, the thickness ofwhich is equal to each other.

According to a third aspect of the present invention, there is provideda magnetic impedance element as defined in the first aspect of thepresent invention, characterized in that the thickness of the laminatedmagnetic films is ununiform.

According to a fourth aspect of the present invention, there is provideda magnetic impedance element as defined in the first aspect of thepresent invention, characterized in that the plurality of magnetic filmsare laminated through non-magnetic thin-films, and the total amount ofproducts of the thickness and the magnetization amplitudes of therespective odd magnetic films is nearly equal to the total amount ofproducts of the thickness and the magnetization amplitudes of therespective even magnetic films.

According to a fifth aspect of the present invention, there is provideda magnetic impedance element as defined in the first, second, third orfourth aspect of the present invention, characterized in that thenon-magnetic films interposed between the respective magnetic films aremade of an electrically conductive material.

According to a sixth aspect of the present invention, there is provideda magnetic impedance element as defined in the first, second, third orfourth aspect of the present invention, characterized in that thenon-magnetic films interposed between the respective magnetic files aremade of an insulator, and both end portions of the laminated magneticfilms are electrically connected to each other at both end sidesthereof.

According to a seventh aspect of the present invention, there isprovided a magnetic impedance element as defined in the first aspect ofthe present invention, characterized in that said magnetic films thatconstitute the thin-film magnetic care are formed of a plating film madeof at least one selected from a group consisting of NiFe, CoFe, NiFeP,FeNiP, FeCoP, FeNiCoP, CoB, NiCoB, FeNiCoB, FeCoB and CoFeNi.

According to an eighth aspect of the present invention, there isprovided a magnetic impedance element as defined in the first aspect ofthe present invention, characterized in that said magnetic films thatconstitute the thin-film magnetic core are formed of an amorphoussputter film which is made of CoZrNb, FeSiB or CoSiB.

According to a ninth aspect of the present invention, there is provideda magnetic impedance element as defined in the first aspect of thepresent invention, characterized in that said magnetic films thatconstitute the thin-film magnetic core are formed of an NiFe sputterfilm.

In the invention thus structured, there can be provided the thin-filmmagnetic impedance element having a uniaxial anisotropy in the widthwisedirection, in which the non-magnetic films are interposed in themagnetic thin-film to provide at least two layers of the magneticthin-films, with the result that the magnetrostatic coupling allows themagnetization vector of the upper and lower magnetic films to be coupledto each other, thereby coming to a magnetic close state. With thisstate, the inner magnetic energy of the thin-film becomes minimized, andthe thin-film having a two-layer structure is made up of only 180°magnetic domain, as a resultof which the MI effect is larger than thatof the single-layer film. From the above viewpoints, the high-sensitivemagnetic impedance element can be provided.

According to a tenth aspect of the present invention, there is provideda magnetic impedance element including a substrate made of anon-magnetic material and a thin-film magnetic core formed on saidsubstrate and having electrodes an both ends of said thin-film magneticcore in a longitudinal direction thereof, characterized in that at leasttwo of said thin-film magnetic cores are disposed in parallel, and saidrespective thin-film magnetic cores are electrically connected in seriesto each other.

With the above structure in which at least two of said thin-filmmagnetic cores are disposed in parallel, and in case said respectivethin-film magnetic cores are electrically connected in series to eachother. the impedance of the magnetic impedance element can be increasedwithout increasing the entire chip size, thereby being capable ofincreasing a sensor output.

According to an eleventh aspect of the present invention, there isprovided a magnetic impedance element as defined in the tenth aspect ofthe present invention, characterized in that said thin-film magneticcore has a thin-film bias coil and a thin-film negative feedback coilformed through an insulator, said thin-film bias coil and said thin-filmnegative feedback coil are alternately wound on the same plane at agiven interval in the same direction and also they are wound by the samenumber of turns.

The above magnetic impedance element is structured in such a manner thatthe thin-film coil for bias and the thin-film coil for negative feedbackare wound around the thin-film magnetic cores which are disposed inparallel through the insulator. The structure makes it possible tominiaturize the magnetic sensor and to make mass production. Also,because the thin-film coil produced with the above structure isexcellent in coil efficiency, a required bias magnetic field is obtainedwith a small amount of current, and the linearity of an output to themagnetic field can be improved with a small amount of negative feedback.Also, since the thin-film coil for bias and the thin-film coil fornegative feedback are alternately wound on the same plans, the biasmagnetic field and the negative feedback magnetic field can be uniformlyapplied to the respective portions of the thin-film magnetic cores, tothereby stabilize the characteristics of the magnetic sensor.

According to a twelfth aspect of the present invention, there areprovided two magnetic impedance elements from which a differentialoutput is extracted in such a manner that two longitudinal thin-filmmagnetic cores formed on a substrate made of a non-magnetic material aredisposed in parallel, first and second electrodes are disposed on bothends of the respective thin-film magnetic cores, and a thin-film biascoil and a thin-film negative feedback coil which are alternately woundon the same plane by the same number of turns in the same direction aredisposed on said thin-film magnetic cores at a given interval through aninsulator.

According to a thirteenth aspect of the present invention, there areprovided two magnetic impedance elements as defined in the twelfthaspect of the present invention, characterized in that the respectivethin-film magnetic cores of the two magnetic impedance elements formedon said non-magnetic substrate are formed of at least two thin-filmmagnetic cores which are disposed in parallel and electrically connectedin series with each other.

According to a fourteenth aspect of the present invention, there areprovided two magnetic impedance elements as defined in the twelfthaspect of the present invention, characterized in that in said twomagnetic impedance elements, the respective one electrodes of the firstand second electrodes of the thin-film magnetic cores, the thin-filmbias coil electrode and the thin-film negative feedback coil electrodeare commonly connected to each other.

According to a fifteenth aspect of the present invention, there areprovided a magnetic impedance element in which a longitudinal thin-filmmagnetic core is formed on a substrate made of a non-magnetic material,first and second electrodes are disposed on both ends of said thin-filmmagnetic core in a longitudinal direction thereof, a third electrode isdisposed at a middle point of said thin-film magnetic core and athin-film bias coil and a thin-film negative feedback coil which arealternately wound on the same plane at the same number of turns in thesame direction are disposed on said thin-film magnetic core at a giveninterval through an insulator, and a differential output is extractedfrom said first and second electrodes.

Because the above structure makes it possible to produce the magneticsensor element for differential driving, a local magnetic field can beaccurately detected, and also the magnetic sensor element fordifferential driving can be produced without increasing the entire chipsize, thereby being capable of miniaturizing the magnetic sensor andmaking mass production.

According to a sixteenth aspect Of the present invention, there areprovided a magnetic impedance element as defined in the fifteenth aspectof the present invention, characterized in that the respective oneelectrodes of the third electrode of said thin-film magnetic core andthe electrodes of the thin-film bias coil and the thin-film negativefeedback coil are commonly connected to each other.

The above structure can make an interval between the two thin-filmmagnetic cores that form a sensor head constant and narrow and canmanufacture the magnetic sensor element for differential driving withoutincreasing the entire chip size, thereby being capable of miniaturizingthe magnetic sensor and making mass production.

According to a seventeenth aspect of the present invention, there areprovided a magnetic impedance element as defined in any one of thefirst, second and twelfth to sixteenth aspects of the present invention,characterized in that said thin-film magnetic core is formed of aplating film made of at least one selected from a group consisting ofNiFe, CoFe, NiFeP, FeCoP, CoB, NiCoB, FeNiCoB, FeCoB and CoFe.

According to an eighteenth aspect of the present invention, there areprovided a magnetic impedance element as defined in any one of thefirst, second and twelfth to sixteenth aspects of the present invention,characterized in that said thin-film magnetic core is formed of anamorphous sputter film made of any one selected from CoZrNb, FeSiB andCoSiB or an NiFe sputter film.

Further, in the above magnetic impedance element, with the structure inwhich a portion that forms an earth electrode out of the electrode ofthe thin-film magnetic core, the electrode of the thin-film bias coiland the electrode of the thin-film negative feedback coil is madecommon, the number of process for connecting the magnetic impedanceelement to a sensor drive circuit due to wire bonding or the like in asensor module manufacturing process can be reduced.

Also, because the thin-film coil manufactured with the above structureis excellent in coil efficiency, a required bias magnetic field isobtained with a small amount of current, and the linearity of an outputto the magnetic field can be improved with a small Amount of negativefeedback. Also, since the thin-film coil for bias and the thin-film coilfor negative feedback are alternately wound, the bias magnetic field andthe negative feedback magnetic field can be uniformly applied to therespective portions of the thin-film magnetic cores, to therebystabilize the characteristics of the magnetic sensor.

The magnetic impedance element according to the present invention isstructured in such a manner that the thin-film magnetic core is formedon the non-magnetic substrate, and the electrodes are disposed on bothends of the thin-film magnetic core In a longitudinal direction thereof.The magnetic impedance element according to the present invention isstructured by laminating a plurality of magnetic films made of at leastone of a group consisting of NiFe, CoFe, NiFeP, FeNiP, FeCoP, FeNiCoP,CoB, NiCoB, FeNiCoB, FeCoB and CoFeNi. Also, in the case where anamorphous material is selected as the magnetic film, any one of CoZrNb,FeSiB and CoSiB is selected.

The non-magnetic film is disposed between the magnetic films of themagnetic impedance element of the present invention, and thenon-magnetic film is made of an electric conductive material or aninsulator.

At least two thin-film magnetic cores are disposed an the non-magneticsubstrate in parallel, the thin-film bias coil and the negative feedbackcoil are formed on the above thin-film core through the insulator, andthose coils are alternately wound on the same plane in the samedirection. The respective one electrodes of the electrodes provided onthe above thin-film bias coil and the negative feedback coil areconnected to each other. The present invention is structured such thattwo magnetic impedance elements are disposed to extract a differentialoutput.

At least two thin-film magnetic cores which are disposed in parallel onthe above non-magnetic substrate are electrically connected in serieswith each other.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of this invention willbecome more fully apparent from the following detailed description takenwith the accompanying drawings in which:

FIG. 1 is an equation diagram representative of a skin depths δ;

FIG. 2 is an equation diagram representative of the impedance of athin-film MI element;

FIGS. 3A and 3B are model diagrams showing the magnetic domain structureof a magnetic core section of the thin-film MI element, respectively;

FIG. 4 is an equation diagram representative of the value of ΔMO;

FIG. 5 is a model diagram showing the magnetic domain structure of amagnetic core section in accordance with one embodiment of the presentinvention;

FIG. 6 is a model diagram showing the magnetic domain structure of amagnetic core section in accordance with another embodiment of thepresent invention;

FIG. 7 is a characteristic graph showing the supply current frequency ofthe thin-film MI element;

FIG. 8 is a characteristic graph showing an impedance change rate of thethin-film MI element to the applied magnetic field;

FIG. 9 is a model diagram showing the magnetic domain structure of amagnetic core section in accordance with further another embodiment ofthe present invention:

FIG. 10 is a model diagram showing the magnetic domain structure of amagnetic core section in accordance with further another embodiment ofthe present invention;

FIG. 11 is a schematic front view showing the structure of a thin-filmmagnetic impedance element used in the present invention;

FIG. 12 is a cross-sectional view taken along line A-B of FIG. 11;

FIG. 13 is a cross-sectional view taken along line C-D of FIG. 11:

FIG. 14 is a circuit block diagram showing the output detection sectionof a magnetic sensor using the thin-film MI element according to thepresent invention;

FIG. 15 is a characteristic graph showing the sensor output to theapplied magnetic field in the circuit shown in FIG. 14;

FIG. 16 is a circuit block diagram showing a conventional magneticsensor using an MI element formed of a magnetic line;

FIG. 17 is a characteristic graph showing the dependency of the appliedmagnetic field on the impedance change of the magnetic line shown inFIG. 16;

FIG. 18 is a plan view showing the main portion of the magneticimpedance element from which a coil and an insulating film are removedin accordance with another embodiment of the present invention;

FIG. 19 is a plan view showing the main portion of the magneticimpedance element using three thin-film MI cores from which a coil andan insulating film are removed;

FIG. 20 is a plan view showing the main portion of the magneticimpedance element using four of more of the thin-film MI cores fromwhich a coil and an insulating film are removed;

FIG. 21 is a characteristic graph representative of the magnetic fluxdensity of an inner element to a distance of magnetic flux between anouter element and the inner element when three thin-film MI magneticcores are disposed in parallel and a uniform magnetic field is appliedto those elements, by %.

FIG. 22 is a graph showing the magnetic field-to-impedancecharacteristic of the magnetic impedance element when the number of thethin-film MI magnetic core is one, two and three.

FIG. 23 is a plan view showing the arrangement of other elements fromwhich an insulating film is omitted in another embodiment of the presentinvention;

FIGS. 24A to 24E are diagrams showing a process of manufacturing athin-film MI sensor;

FIG. 25 is a circuit diagram showing a magnetic field detection magneticsensor formed of two thin-film MI sensors shown in FIG. 1;

FIG. 26 is a graph showing the output voltage characteristic of themagnetic field detection magnetic sensor shown in FIG. 8;

FIG. 27 is a plan view schematically showing a magnetic impedanceelement (thin-film MI sensor) in accordance with another embodiment ofthe present invention:

FIG. 28 is a plan view schematically showing a magnetic impedanceelement (thin-film MI sensor) with the structure where an earth terminalis commonly used;

FIG. 29 is a plan view schematically showing a magnetic impedanceelement (thin-film MI sensor) in which a third electrode is disposed atthe middle point of the thin-film magnetic core;

FIG. 30 is a plan view schematically showing a magnetic impedanceelement (thin-film MI sensor) in which the earth terminal of thethin-film MI sensor with the structure shown in FIG. 29 is commonlyused;

FIG. 31 is a plan view schematically showing a magnetic impedanceelement (thin-film MI sensor) in which each of two thin-film magneticcores is made up of two thin-film magnetic cores;

FIG. 32 is a graph showing the magnetic field-to-impedancecharacteristic of the magnetic impedance element shown in FIG. 27;

FIG. 33 is a graph showing the external magnetic field-to-amplitudecharacteristic when a positive bias magnetic field is applied to one oftwo MI elements (for example, the thin-film MI element on the upper sideof FIG. 1);

FIG. 34 is a graph showing the external magnetic field-to-amplitudecharacteristic when a positive bias magnetic field is applied to theother of two MI elements (for example, the thin-film MI element on thelower side of FIG. 1);

FIG. 35 is a graph showing the output voltage characteristic of themagnetic field detection magnetic sensor in accordance with the presentinvention; and

FIG. 36 is a graph showing the temperature-to-output fluctuationcharacteristic of the magnetic field detection magnetic sensor inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a description will be given in more detail of preferredembodiments of the present invention with reference to the accompanyingdrawings.

The magnetic impedance effect (MI effect) is directed to a phenomenon inwhich when a high-frequency current is supplied to a magnetic substanceof the high magnetic permeability, an impedance between both endsthereof varies according to an external magnetic field applied to thecurrent supply direction. In other words, the magnetic impedance effectis caused by the fact that the impedance Z due to the internalinductance Li of the magnetic substance and the resistance Rw whichincreases together with the frequency f of an applied current due to theskin effect varies as a function of the magnetic permeability μ in thewidthwise direction of the magnetic substance which varies by applying amagnetic field from the external.

Z=Rw(μθ)+jωLi(μθ)  (1)

In case of a thin-film, the resistance Rw of the thin-film in ahigh-frequency band (film thickness d>>2δ) where the skin effect isremarkable can be represented by the following expression assuming thatthe d.c. resistance is Rdc.

Rw=Rdc(d/2δ)

On the other hand, in case of d>>2δ, the inductance can be representedby the following expression.

L=Li(2δ/d)

where δ is a skin depth having a value shown in FIG. 1. Accordingly, theimpedance of the thin-film is represented as follows:

Z=Rdc(d/2δ)+jωLi(2δ/d)

The impedance of the thin-film is obtained as shown in FIG. 2 assumingthat the thickness of the thin-film d is 2 a, the width is W and thelength is 1.

In this case, since the skin depth δ is obtained as shown in FIG. 1, theimpedance Z of the thin-film is a function of the magnetic permeabilityμθ.

When a uniaxial anisotropy is given in the widthwise direction of thethin-film pattern as shown in FIG. 3A, the magnetic vector is toward thewidthwise direction, and the magnetic domain structure is of thestructure having 180° magnetic wall. By the way, in the case ahigh-frequency current flows in the longitudinal direction of thethin-film, although a high-frequency magnetic field is developed in thewidthwise direction, the movement of the 180° magnetic wall is preventedby an eddy current damping. Also, because the high-frequency magneticfield direction and the magnetization vector direction are identicalwith each other, it is difficult that a rotating magnetization occurs.For that reason, a change in the magnetic flux is small, and themagnetic permeability μθ is small.

On the other hand, when the external magnetic field Hex is applied inthe longitudinal direction of the thin-film pattern, the direction ofthe magnetization vector is inclined from the widthwise direction.Accordingly, since the rotation of the magnetization vector (rotatingmagnetization) occurs due to the magnetic field caused by thehigh-frequency current to change the magnetic flux, the magneticpermeability μθ becomes large. When the external magnetic field Hexbecomes identical with the anisotropic magnetic field Hk of the filmpattern, the magnetic permeability μθ becomes the largest, where theimpedance Z becomes maximum. When the external magnetic field Hexbecomes further large (Hex>Hk), the magnetization vector is fixed toHex. Therefore, the rotation of the magnetization vector is restrained,and the magnetic permeability μθ becomes smaller, as a result of whichthe impedance Z becomes also smaller.

Those phenomenons will be proved on the basis of the rotatingmagnetization model with reference to FIG. 3B. In case of H θ=0, therotating angle θ0 is determined under the energy minimizing conditionrepresented by the following expression.

E0=−Ku cos 2(π/2−θ0)−Ms Hex cos θ0  (3)

Therefore,

θ0=Hex/Hk is obtained from Hk=2 Ku/Ms. where assuming that a change ofthe rotating angle due to H θ is Δθ<<θ0, the magnetic change M in thewidthwise direction is represented by the following expression.

ΔM=Ms cos θ0Δθ  (4)

Also, the total energy including a term of Hθ is represented by thefollowing expression.

E=−Ms(Hθ+Hk) cos [π/2−(θ0+Δθ)]−Ms Hex cos (θ0+Δθ)  (5)

If using the expression (5), Δθ is obtained from the expression (7)shown in FIG. 4 and substituted for the expression (4), the expression(6) shown in FIG. 4 is obtained.

Accordingly, in Hex<Hk, the magnetic permeability μθ, that is, theimpedance Z increases more as the magnetic field increases, and afterthe maximum value is taken in Hex=Hk, the impedance Z is reduced more asthe magnetic field increases.

Also, when the magnetization vector is toward the longitudinal directionof the thin-film pattern, since the magnetic permeability μθ in thewidthwise direction due to the external magnetic field Hex hardlychanges, the MI effect becomes very small.

By the way, a magnetic domain structure shown in FIG. 3A is ideal, andin fact, when a uniaxial anisotropy is given in the widthwise directionof a single-layer thin-film pattern, a demagnetizing field is developedin the widthwise direction, and in order to minimize the demagnetizingfield energy, the magnetic domain structure becomes a state where themagnetization vector is closed as shown in FIG. 5. With this magneticdomain structure, the internal magnetization energy of the magneticthin-film becomes minimum and stabilized.

However, as described above, when the magnetization vector is directedto the longitudinal direction of the thin-film pattern, since a magneticpermeability μθ in the widthwise direction due to the external magneticfield Hex is hardly changed, the MI effect becomes very small. In otherwords, the MI effect of the 90° magnetic domain portion shown in FIG. 5is very small so that the MI effect of the entire thin-film becomessmall.

As shown in FIG. 6, a uniaxial anisotropy is given in a widthwisedirection, and a non-magnetic film is inserted into the middle of themagnetic thin-film to structure two layers of the non-magnetic film withthe result that the magnetrostatic coupling allows the magnetizationvector of the upper and lower magnetic films to be coupled to eachother, thereby coming to a magnetic closed state. With this state, theinternal magnetization energy of the thin-film becomes minimized andstabilized. Also, the thin-film having a two-layer structure is made upof only 180° magnetic domain, as a result of which the MI effect islarger than that of the single-layer film,

The magnetic film of the magnetic impedance element shown in FIG. 6 maybe formed of an amorphous sputter film made of CoZrNb, FeSiB, CoFeB, orthe like or a soft magnetic film such as an NiFe sputter film. Forexample, an example in which the NiFe sputter film is used will bedescribed. An NiFe sputter film is formed in thickness of about 2.5 μmon a non-magnetic and insulating substrate, a non-magnetic film made ofTi or the like is further formed in thickness of about 10 nm on thesputter film. and an NiFe sputter film is finally formed in thickness ofabout 2.5 μm on the non-magnetic film. Thereafter, a photoresist patternhaving a predetermined magnetic core configuration is formed on thethin-film. The thin-film is etched by etching means such as ion mealingwhile the photoresist pattern is used as an etching mask. Then, thephotoresist pattern is removed by an organic solvent or the like, thusproducing a magnetic impedance element.

The thickness of the non-magnetic film thus produced is required to beset to the degree where the exchange coupling of the upper and lowermagnetic films can be blocked, and the thickness may be about 10 nm ormore In addition, because the MI element employs the magneticpermeability dependency of the skin effect, it is desirable to use anelectrically conductive thin-film made of Ti, Ta, Cu, Al, Au, Ag, Pt orthe like as the intermediate non-magnetic film. Incidentally, in thecase where the non-magnetic film is formed of an insulating thin-film,both end portions of the laminated magnetic films are electricallyconnected to each other at both end sides so that the laminated magneticfilms are electrically connected in parallel.

Also, in order to couple the magnetization vectors of the upper andlower magnetic films together to minimize the entire internal magneticenergy, it is necessary to make the total amounts of the magnetizationsof the upper and lower magnetic films equal to each other. To achievethis, it is necessary to satisfy the condition of. Ms1×t1=Ms2×t2assuming that the magnetization of the upper magnetic film is Ms1, thethickness of the upper magnetic film is t1, the magnetization of thelower magnetic film is Ms2 and the thickness of the lower magnetic filmis t2.

FIG. 7 is a graph showing the frequency characteristic of the sensorboth-end electrode E (E=Z * I) when an external magnetic field (Hex) of0 and 2.4 kA/m is applied in the longitudinal direction of the elementto a thin-film magnetic impedance element produced with the structure oftwo NiFe sputter films about 2.5 μm in thickness while Ti is used as theintermediate film. A difference ΔE of E at the time of Hex=0 and Hex=2.4kA/m was maximum when the frequency of the supply current is about 20MHz.

FIG. 8 shows a dependency of the impedance change rate on the appliedmagnetic field (Hex) when the frequency of applied current of 20 MHz (10mA) is constantly applied to a two-layer thin-film magnetic impedanceelement (2.5 μm×2-layer) made of NiFe. For comparison, thecharacteristic of a single-layer thin-film magnetic impedance element (5μm) made of NiFe is shown together. As the applied magnetic fieldincreases, the change rate ΔZ/Z0 of the impedance increases more, andΔZ/Z0 becomes maximum when the applied magnetic field is the anisotropymagnetic field Hk of the element, and ΔZ/Z0 reduces when Hex>Hk. Thoseresults become the characteristic represented by the above-mentionedtheoretical expression. Also, the change rate of the impedance of thetwo-layer film magnetic impedance element is large, that is, 90% ascompared with that of the single-layer film magnetic impedance elementbeing 75%. At this time, the change amount (magnetic field sensitivity)of the impedance per a unit applied magnetic field becomes maximum whenHex is about 1.6 kA/m and exhibits the magnetic field sensitivity of0.08%/(A/m).

Also, a method of manufacturing the thin-film magnetic impedance elementin accordance with another embodiment of the present invention will bedescribed. The reverse configuration of a given thin-film magnetic coreis prepared in a thin metal plate, and a non-magnetic substrate ismasked with the metal plate as a sputter mask. Then, an NiFe sputterfilm is formed in thickness of about 2.5 μm, a non-magnetic film made ofTi or the like is formed in thickness of about 10 nm and a NiFe sputterfilm is further formed in thickness of about 2.5 μm, to manufacture amagnetic impedance element.

An embodiment in which a plating film made of any one of NiFe, CoFe,NiFeP, FeNiP, FeCoP, FeNiCoP, CoB, NiCoB, FeNiCoB, FeCoB, CoFeNi and soon is used as a magnetic film will be described. First, an NiFe sputterfilm having a thickness of about 50 nm is formed as a seed layer forplating. A photoresist pattern of the reverse pattern having a givencoil configuration is formed on the seed layer, and an NiFe plating isembedded in thickness of about 2.5 μm between the photoresist pattern.Then, a non-magnetic metal made of Cu or the like is deposited inthickness of about 10 nm thereon through a plating method. Further, anNiFe plating is embedded in thickness of about 2.5 μm thereon.Thereafter, the photoresist pattern is removed by an organic solvent orthe like, and a magnetic impedance element is formed by removing theseed layer of the NiFe plating film by etching. The magnetic impedanceelement is manufactured through the same process even when the platingfilm made of CoFeNi or the like is used as a thin-film magnetic core.

Also, all the thin-film magnetic cores manufactured in theabove-mentioned methods improve the magnetic characteristics if they aresubjected to a heat treatment during the rotating magnetic field and thestatic magnetic field after being manufactured.

In a multi-layer film of three layers or more, that is, in a structurewhere n-layers (n≧3) are laminated through non-magnetic thin-films, thenon-magnetic films between the films are an electrically conductivematerial and when the total amount of products of the thickness and themagnetization amplitudes of the respective odd magnetic films is nearlyequal to the total amount of products of the thickness and themagnetization amplitudes of the respective even magnetic films, themagnetization vector of the magnetic films of the respective layersmakes magnetrostatic coupling, and the internal magnetization energy ofthe thin-film is minimized and stabilized. Also, the thin-film havingthe multi-layer structure which satisfies the above condition isstructured by only 180° magnetic domain with the result that the MIeffect becomes larger than that of the single-layer film.

FIG. 9 shows an embodiment of a three-layer structure, and in thisembodiment, assuming that the magnetization of the uppermost magneticfilm is Ms1, the thickness of the uppermost magnetic film is t1, themagnetization of the second magnetic film is Ms2, the thickness of thesecond magnetic film is t2, the magnetization of the lowermost magneticfilm is Ms3 and the thickness of the lowermost magnetic film is t3, whenMs1×t1 +Ms3×t3=Ms2×t2 is satisfied, the magnetization vectors of therespective magnetic layers make magnetrostatic coupling, and thethin-film is made up of only 180° magnetic domain.

FIG. 10 shows an embodiment of a four-layer structure, and in thisembodiment, assuming that the magnetization of the uppermost magneticfilm is Ms1, the thickness of the uppermost magnetic film is t1, themagnetization of the second magnetic film is Ms2, the thickness of thesecond magnetic film is t2, the magnetization of the third magnetic filmis Ms3, the thickness of the third magnetic film is t3, themagnetization of the fourth magnetic film is Ms4 and the thickness ofthe fourth magnetic film is t4, when Ms1×t1+Ms3×t3=Ms2×t2+Ms4×t4 issatisfied, the magnetization vectors of the respective magnetic layersmake magnetrostatic coupling, and the thin-film is made up of only 180°magnetic domain.

Also, although being not shown, in case of an n-layer structure,assuming that the magnetization of the uppermost magnetic film is Ms1,the thickness of the uppermost magnetic film is t1, the magnetization ofthe second magnetic film is Ms2, the thickness of the second magneticfilm is t2, . . . the magnetization of the n-th magnetic film is Msn andthe thickness of the n-th magnetic film is tn, when it is satisfied thatthe total amount of products of the thickness and the magnetizationamplitudes of the respective odd magnetic films is nearly equal to thetotal amount of products of the thickness and the magnetizationamplitudes of the respective even magnetic films, the magnetizationvectors of the respective magnetic layers make magnetrostatic coupling,and the thin-film is made up of only 180° magnetic domain.

Subsequently, the characteristic of the thin-film magnetic impedanceelement which has been manufactured using a two-layer thin-film magneticimpedance element will be described. FIG. 11 is a schematic front viewshowing the structure of a thin-film magnetic impedance (MI) elementused in the embodiment of the present invention, FIG. 12 is across-sectional view taken along line A-B of FIG. 11, and FIG. 13 is across-sectional view taken along line C-D of FIG. 11. Although theactual entire thin-film MI sensor is formed on a thin-film ceramic plateor a plate body such as a glass plate, such a plate is omitted from FIG.11. Referring to FIGS. 11, 12 and 13, reference numeral 1 denotes an MIsensor plate which is a thin-film magnetic core shaped in a thin-filmrectangular in plane configuration. The configuration of the thin-filmmagnetic core as the MI sensor plate is 20 μm in width, 5 μm inthickness and 500 μm in length. A bias coil 4 and a negative feedbackcoil 5 are alternately wound around the MI sensor plate 1 throughinsulating layers 2 and 3 in the same direction. Although being notaccurately shown in the figures, the number of turns of those coils is20, respectively. With the structure in which the coils for bias andnegative feedback are alternately wound around the thin-film magneticcore on the same plane, a bias magnetic field and a negative feedbackmagnetic field can be uniformly applied to the respective portions ofthe magnetic core, to thereby improve the linearity of the sensitivecharacteristic as a magnetic sensor. Both ends of the bias coil 4 areconnected with bias coil terminals 6 and 7, and both ends of thenegative feedback coil 5 are connected with negative feedback coilterminals 8 and 9. Both ends of the MI sensor plate 1 are connected withMI sensor terminals 10 and 11. Those terminals are formed of Au metalthin-films, and those widened tip portions serve as pads for externalwiring. Incidentally, reference numeral 12 denotes an insulatingprotective film that covers the entire MI sensor.

When the thin-film magnetic impedance element is used as a magneticsensor, the operating point is brought to the maximum sensitivity,thereby being capable of improving the sensor sensitivity. For thatreason, if a current is allowed to flow into the bias coil, a biasmagnetic field is applied to the magnetic impedance element, therebybeing capable of changing the operating point, and the application ofthe bias magnetic field of 1.6 kA/m to the magnetic core using thethin-film coil makes the magnetic field sensitivity maximum at a portionwhere the applied magnetic field is 0.

On the other hand, in the case where the operating point is moved usingthe bias coil so that the magnetic field sensitivity becomes maximumwhen the applied magnetic field is 0, the linearity of a change of theimpedance (a change in output) to the magnetic field is notsatisfactory. As a method for improving the linearity, there is applieda method in which an output signal is fed back, and a magnetic fieldnecessary only for correcting the non-linearity of the output to themagnetic field is applied to the thin-film magnetic core as the negativefeedback magnetic field by using the negative feedback coil, therebycorrecting the output signal to obtain the linearity. FIG. 14 is a blockdiagram showing an electronic circuit in an output detecting section ofa linear magnetic field MI sensor. Due to this circuit, the operatingpoint is moved to a point of the maximum sensitivity, the output signalis fed back and a negative feedback magnetic field is applied to thethin-film core, thereby enhancing the linearity of the characteristic ofthe sensitivity.

FIG. 15 shows a relation of the output voltage to the applied magneticfield when 1.6 kA/m in bias coil magnetic field and 50% in negativefeedback ratio is effected by using the circuit shown in FIG. 14. Inthis example, the frequency of the supply current is 20 MHz, and theamplification degree of the output is 500 times. As shown in the figure,the excellent linearity is exhibited within the measured magnetic fieldof ±240 μA/m, and the magnetic resolution of 10⁻⁴ A/M is exhibited.Those results are excellent characteristics as the linear magnetic fieldsensor.

Subsequently, a description will be given of another embodiment of thepresent invention in which two or more thin-film magnetic cores aredisposed in parallel on a substrate made of a non-magnetic substance andconnected in series with each other. This embodiment corresponds to theinventions of claims 10 to 11.

FIG. 18 is a schematic view showing the structure of a thin-film MIsensor 54 (magnetic impedance element) in accordance with thisembodiment. In the thin-film MI sensor 54, two thin-film MI magneticcores 55 are disposed in parallel at an interval of 20 μm, and therespective cores 55 are electrically coupled in series with each otherby a non-magnetic conductor 56 made of Cu or the like. In this example,because the total length of the magnetic core (thin-film MI magneticcore 55) can be lengthened double without lengthening the overall lengthof the sensor element (thin-film Ml sensor 54), the impedance becomestwice, and because an external magnetic field is uniformly applied totwo magnetic cores the sensor sensitivity (the sensitivity of thethin-film MI sensor 4) becomes double. The core 55 is formed on thesubstrate made of a non-magnetic substance not shown (refer to anon-magnetic substrate 70 in FIG. 24).

In FIG. 18, the thin-film MI magnetic core 55 is formed of a platingfilm (soft magnetic film) made of at least one kind selected from agroup consisting of NiFe, CoFe, NiFeP, FeNiP, FeCoP, FeNiCoP, CoB,NiCoB, FeNiCoB, FeCoB and CoFe. The thin-film MI magnetic core 55 may beformed of an amorphous sputter film made of any one of CoZrNb, FeSiB andCoSiB, or an NiFe sputter film (soft magnetic film).

Subsequently, a manufacturing example when the NiFe plating film is usedas the thin-film magnetic core (thin-film MI magnetic core 55) will bedescribed.

First, an NiFe sputter film having a thickness of about 200 nm is formedas a seed layer for plating. A photoresist pattern of the reversepattern having a given coil configuration is formed on the seed layer,and thereafter an NiFe plating is embedded in thickness of about 3 μmbetween the photoresist pattern. Then, after the photoresist pattern isremoved by an organic solvent or the like, the seed layer of the NiFesputter film is removed by etching to form the thin-film magnetic core.The thin-film magnetic core is manufactured through the same processeven when a CoFeNi plating film is used as a thin-film magnetic core(thin-film MI magnetic core 55). The magnetic characteristics areimproved if the magnetic impedance element is subjected to a heattreatment during the rotating magnetic field and the static magneticfield after the thin-film magnetic core has been manufactured.

Referring to FIG. 18, reference numeral 57 denotes an electrode forallowing a high-frequency current to flow in the thin-film MI element(thin-film MI sensor 4). Also, as described above, the non-magneticconductor 56 made of Cu or the like is a conductor for electricallyconnecting two thin-film MI magnetic core 55 in series. However, thenon-magnetic conductor 56 may be a non-magnetic low-resistant conductormade of Au, Al, or the like, A case in which the non-magnetic conductor56 is made of Cu will be described. A Cu sputter film having a thicknessof about 50 nm is formed as a seed layer for plating. Then, after aphotoresist pattern of the reverse pattern having a given coilconfiguration has been formed on the seed layer, a Cu plating isembedded In thickness of about 3 μm into the photoresist pattern, andfurther after the photoresist pattern has been removed by an organicsolvent or the like, the seed layer of the Cu sputter film is removed byetching to form the thin-film MI element.

Also, a lower-layer coil portion may be manufactured in the followingmanner. That is, the Cu sputter film is formed in thickness of about 3μm, and thereafter a photoresist pattern having a coil configuration isformed. The Cu sputter film is etched by etching means such as ionsealing with the photoresist pattern as an etching mask, and further thephotoresist pattern is removed by an organic solvent or the like to formthe lower-layer coil portion. A wire bonding pad made of Au is formed onan end portion of the conductive portion. Thereafter, the lower-layercoil portion is cut into a plurality of chips by a slicer. The chip sizeis 2.3 mm×1.2 mm.

FIG. 18 shows the thin-film MI sensor 54 using two thin-film MI magneticcores 55. Alternatively, as shown in FIG. 19, three thin-film MImagnetic cores 55 are disposed in parallel to constitute the thin-filmMI sensor 54, or as shown in FIG. 20, four of more of the thin-film MImagnetic cores 55 are disposed in parallel to constitute the thin-filmMI sensor 54.

In FIGS. 19 and 20, an interval between the thin-film MI magnetic cores55 disposed in parallel is 20 μm and the respective thin-film MImagnetic cores 55 are electrically coupled in series with each other bya non-magnetic conductor 56 made of Cu or the like. Incidentally, whenthree or more elements (thin-film MI magnetic cores 55) are closelydisposed in parallel, there is a fear that an element (thin-film MImagnetic core 55) positioned at the outermost side and an element(thin-film MI magnetic core 55) positioned at the innermost sidemagnetically interfere with each other, as a result of which a magneticfield is not uniformly applied to the respective elements.

FIG. 21 is a graph showing a difference in magnetic flux between theouter element and the inner element when a magnetic field is uniformlyapplied to the respective elements in a state where three elements(thin-film MI magnetic cores 55) are disposed in parallel. In thefigure, the magnetic flux density of the inner element to the outerelement is represented by % when the intervals between the respectiveelements are changed. As the interval between the respective elements isnarrower, an influence of interference is found. However, the differencein magnetic flux between the outer and inner elements is about 3% evenwhen the interval is 5 μm, for example, which does not almost cause anyproblem.

FIG. 22 shows the magnetic field-impedance characteristic of thethin-film MI sensor 54 (FIG. 8) in which two thin-film MI magnetic cores55 are disposed in parallel, and the respective thin-film MI magneticcores 55 are electrically connected in series with each other, and thethin-film MI sensor 54 (FIG. 19) in which three thin-film MI magneticcores 55 are disposed in parallel, and the respective thin-film MImagnetic cores 55 are electrically connected in series with each other.In this case, the measured current is a sine wave of 20 MHz and 40mAp-p. FIG. 22 also shows the characteristic in case of one thin-film MImagnetic core 55 for comparison. The output value of the thin-film MIsensor 54 in which two or three thin-film MI magnetic cores 55 wereconnected in series was twice or three times as large as that in case ofone thin-film MI magnetic core 55.

Subsequently, the above second embodiment of the present invention willbe described with reference to FIGS. 23 to 26.

FIG. 23 is a plan view showing the arrangement of elements other thanthe insulating film in the structure of the thin-film MI sensor 54according to the prevent invention.

The configuration of the thin-film MI magnetic core 55 in the thin-filmMI sensor 54 is 20 μm in width, 3 μm in thickness and 2000 μm in length,and the bias thin-film coil 61 and the negative feedback thin-film coil62 are wound around the thin-film magnetic core (thin-film MI magneticcore 55) through the insulating film 60 three-dimensionally. The biasthin-film coil 61 and the negative feedback thin-film coil 62 arealternately wound, and the number of turns is 42, respectively. Also, anAu pad for wire bonding is provided on a part of the respectiveelectrode portions.

FIGS. 24A to 24E show a process of manufacturing the thin-film MI sensor54 which is represented by a cross-sectional view of FIG. 23 along thelongitudinal direction thereof. Then, the detailed structure and themanufacturing process of the thin-film MI sensor 54 will be describedwith reference to FIGS. 24A to 24E.

The thin-film process of FIG. 24A to 24E is made In the order tomanufacture the thin-film MI sensor 54.

FIG. 24A shows the coil lower-layer portion (lower layer coil portion71) that constitutes the bias thin-film coil 61 and the negativefeedback thin-film coil 62, in which the end portions of the respectivecoil portions are connected to the coil end portions of the coilupper-layer portions 72 shown in FIG. 24E to constitute the continuousbias thin-film coil-61 and negative feedback thin-film coil 62.

The lower-layer coil portion 71 is formed on the non-magnetic substrate70 having the enhanced surface flatness which is formed of an A1203ceramic wafer, an Si wafer, a glass wafer or the like to form the Cusputter film about 50 nm in thickness as a seed layer for plating. Then,after a photoresist pattern of the reverse pattern having a given coilconfiguration has been formed on the seed layer, a Cu plating isembedded in thickness of about 3 μm into the photoresist pattern, andfurther after the photoresist pattern has been removed by an organicsolvent or the like, the seed layer of the Cu sputter film is removed byetching to form the thin-film MI element. On the other hand the Cusputter film is formed in thickness of about 3 μm, and a photoresistpattern having a given coil configuration is then formed thereon.Thereafter, the Cu sputter film is etched by etching means such as ionmealing with the photoresist pattern as an etching mask, and further thephotoresist pattern is removed by an organic solvent or the like to formthe lower-layer coil portion 71.

The above method of preparing the Cu coil (bias thin-film coil 61 andnegative feedback thin-film coil 62) enables the coil per se to beminiaturized and enables the coil to approach the magnetic core(thin-film MI magnetic core 55), thereby allowing the coil efficiency tobe enhanced as compared with a method of preparing a coil by winding aconductive wire and a method of preparing a coil by winding a conductivethin band.

Reference numeral 60 a in FIG. 24B is an insulating film forelectrically insulating the lower-layer coil portion and the thin-filmmagnetic core. The insulating film 60 a results from subjecting theinsulating film 60 a to a heat treatment at 270° C. for 10 hours forhardening after exposure and development processes are conducted on aphotoresist to form the insulating film 60 a having a givenconfiguration. Alternatively, a resin such as polyimide which has beenhardened or an inorganic film such as SiO₂ which has been formed in agiven configuration may be employed.

Reference numeral 55 in FIG. 24C denotes the thin-film MI magnetic corewhich is formed of a plating film (soft magnetic film) made of at leastone material selected from a group consisting of NiFe, CoFe, NiFeP,FeNiP, FeCoP, FeNiCoP, CoB, NiCoB, FeNiCoB, FeCoB and CoFe. Thethin-film MI magnetic core 55 may be formed of an amorphous sputter film(soft magnetic film) made of any one of CoZrNb, FeSiB and CoSiB, or anNiFe sputter film (soft magnetic film).

Now, a manufacturing example in which the NiFe plating film is used asthe thin-film MI magnetic core 55 will be described. First, an NiFesputter film having a thickness of about 50 nm is formed as a seed layerfor plating. A photoresist pattern of the reverse pattern having a givencoil configuration is formed on the seed layer, and thereafter an NiFeplating is embedded in thickness of about 3 μm into the photoresistpattern. Then, after the photoresist pattern is removed by an organicsolvent or the like, the seed layer of the NiFe sputter film is removedby etching to form the thin-film magnetic core. The thin-film magneticcore is manufactured through the same process even when a CoFeNi platingfilm is used as a thin-film MI magnetic core 55. The magneticcharacteristics are improved if the magnetic impedance element issubjected to a heat treatment during the rotating magnetic field and thestatic magnetic field after the thin-film MI magnetic core 55 has beenmanufactured.

Subsequently, a manufacturing process in which a soft magnetic film suchas an amorphous sputter film made of CoZrNb, FeSiB, CoFeB, or the likeor an NiFe sputter film is used as the thin-film MI magnetic core 55will be described. For example, a lower-layer coil portion 71 may bemanufactured In the following manner. That is, the CoZrNb sputter filmis formed in thickness of about 3 μm, and thereafter a photoresistpattern having a given magnetic core configuration is formed on thesputter film. The sputter film is etched by etching means such as ionmealing with the photoresist pattern as an etching mask, and further thephotoresist pattern is removed by an organic solvent or the like to formthe lower-layer coil portion 71. on the other hand, there is a metalmask method in which the reverse configuration of a given thin-film MImagnetic core 55 is manufactured in a thin metal plate and used as asputter mask. However, this method is not preferred because it isdifficult to obtain a magnetic core having a fine configuration, and thedimensional accuracy is low.

Reference numeral 60 b in FIG. 24D denotes an insulating film forelectrically insulating the upper-layer coil portion (coil upper-layerportion 72) and the thin-film MI magnetic core 55. The manufacturingmethod of the insulating film is the sama as that in case of theinsulating film 60 a shown in FIG. 24B.

FIG. 24E shows the coil upper-layer portion 72 that constitutes the biasthin-film coil 61 and the negative feedback thin-film coil 62, in which.as described with reference to FIG. 24A, the end portions of therespective coil portions are connected to the coil end portions of thecoil lower-layer portions (lower layer coil portions 71) shown in FIG.24A to constitute the continuous bias thin-film coil 61 and negativefeedback thin-film coil 62. The manufacturing method is the same as thatin case of the coil shown in FIG. 24A.

Finally, although being not shown, a protective layer that protects themanufactured magnetic sensor portion and a bonding pad for wire bondingfor obtaining electric connection between peripheral circuits fordriving and sensing the magnetic sensor is manufactured. The protectivelayer results from subjecting the protective film to a heat treatment at270° C. for 10 hours for hardening after exposure and developmentprocesses are conducted on a photoresist to form the insulating film 60a having a given configuration. Alternatively, a resin such as polyimidewhich has been hardened or an inorganic film such as SiO₂ which has beenformed in a given configuration may be employed. The Au pad for wirebonding which is provided on one part of the electrode portion is formedof an Au plating film or an Au sputter film. The manufacturing method isnearly the same as that in case of the Cu coil.

Then, the characteristic of the manufactured thin-film MI sensor 54 willbe described. In this example, the dimensions of the thin-film MImagnetic core 55 are 20 μm in width, 3 μm in thickness and 2000 μm inlength, and two thin-film MI magnetic cores 55 are connected in series.The chip size of the element is 2.3 mm×0.8 mm. Also, the bias thin-filmcoil 61 and the negative feedback thin-film coil 62 are alternatelywound on the same surface, and the number of turns is 42, respectively.With the structure in which the bias thin-film coil 61 and the negativefeedback thin-film coil 62 are alternately wound around the thin-film MImagnetic core 55 on the same surface, a bias magnetic field and anegative feedback magnetic field can be uniformly applied to therespective portions of the thin-film MI magnetic core 55, to therebystabilize the characteristic as the magnetic sensor (thin-film MI sensor54).

A magnetic field detection magnetic sensor 81 is structured such thattwo thin-film MI sensors 54 shown in FIG. 23 are so disposed as toenable differential drive, and the magnetic sensor circuit system ismade up of a differential drive circuit 80 shown in FIG. 25. Themagnetic field detection magnetic sensor 81 includes an oscillatingcircuit portion 82 that supplies a high-frequency current to those twothin-film MI sensors 54. The differential drive circuit 80 is made up ofa detecting circuit section 83 having a detector (reference omitted)consisting of diodes D1-1, D1-2, D2-1, D2-2 and so on, and an amplifiersection 84 that differentially amplifies a signal from the detectingcircuit section 83 to output the amplified signal. The output section ofthe amplifier section 84 and the negative feedback thin-film coil 62 areconnected to each other through the negative feedback section 85 in sucha manner that the output signal from the amplifier section 84 isnegatively fed back to the negative feedback thin-film coil 62.

FIG. 26 shows a relation of the output voltage of the sensor (magneticfield detection magnetic sensor 81) to the applied magnetic field when anegative feedback 240 A/m in bias coil magnetic field and 40% innegative feedback ratio is effected using the magnetic field detectionmagnetic sensor 81. In this example, the supply current is of a pulsewave having 5 ns pulse width, the pulse current is 35 mA and theamplification degree of the output is 25 times. As shown in the figure,the output when two magnetic cores (thin-film MI magnetic core 55) aredisposed in parallel and connected in series is twice as large as thatin case of one magnetic core (thin-film MI magnetic core 55) measured ascomparison. Likewise, the output when three magnetic cores (thin-film MImagnetic core 55) are disposed in parallel and connected in series isthree times as large as that in case of one magnetic core (thin-film MImagnetic core 55). The chip size is 2.3 mm×1.2 mm which is identicalwith the chip size of one magnetic core.

The sensor characteristic exhibits the linearity excellent within themeasured magnetic field of ±80 A/m and exhibits the magnetic fieldresolution of 10⁻³ A/m. Those results exhibit the excellentcharacteristic as the linear magnetic field sensor. Also, in case of theelement using a negative feedback coil in which a copper wire is woundaround an amorphous wire, in order to obtain the same linearity as thatof FIG. 26, a negative feedback of about 300% must be effected. Thereason that the thin-film coil has the same linearity as that of thenegative feedback coil where the copper wire is wound around theamorphous wire with the negative feedback ratio of about ⅙ is that thecoil is allowed to approach the magnetic core (thin-film MI magneticcore 55) with the result that the coil efficiency of the thin-film coilis enhanced as described with reference to the bias coil.

Further, another embodiment of the present invention will be describedwith reference to the attached drawings.

FIG. 27 is a plan view schematically showing the structure of athin-film magnetic impedance sensor (thin-film MI sensor 103) which isan example of the magnetic impedance element according to the presentinvention.

The thin-film MI sensor 103 has two thin-film magnetic cores 1 shown inFIG. 11. The dimensions of one thin-film magnetic core 104 are 20 μm inwidth, 3 μm in thickness and 2000 μm in length. Although the structureof one thin-film magnetic core 104 is identical with that shown in FIG.11, the bias thin-film coil 105 (thin-film bias coil) and the negativefeedback thin-film coil 106 (thin-film feedback coil) constitute onethin-film MI element 103 a in cooperation with a common substrate(corresponding to the non-magnetic substrate 70 in FIG. 24). The numberof turns of the bias thin-film coil 105 and the negative feedbackthin-film coil 106 is 42, respectively. Two thin-film Ml elements 103 astructured as described above are disposed on the common substrate notshown so as to form one chip (in other words, one chip has the functionof two magnetic impedance elements and constitutes a compound magneticimpedance element.), and the dimensions of the chip are 2.3 mm×1.6 mm.

A first electrode 107 and a second electrode 108 are disposed on bothends of the respective thin-film magnetic cores 104 in the longitudinaldirection thereof so that a differential output may be extracted fromthe respective thin-film magnetic cores 104. Also, as is apparent fromthe above description of the thin-film MI sensor manufacturing processshown in FIG. 24, the bias thin-film coil 105 (thin-film bias coil) andthe negative feedback thin-film coil 106 (thin-film negative feedbackcoil) are alternately wound on the same plane at a given intervalthrough an insulating film 600 (insulator) in the same direction and asdescribed above, the same number of turns. In the thin-film MI sensor103 shown in FIG. 27, the first electrode 107 is grounded (that is, thefirst electrode 107 is set as an earth terminal). The thin-film MIsensor 103 shown in FIG. 28 is of the structure in which the earthterminals (first electrode 107, one terminal of the bias thin-film coil105 and one terminal of the negative feedback thin-film coil 106) of thethin-film MI sensor 103 structured as shown in FIG. 27 are made common,whereby the number of terminals connected to the sensor drive circuit isreduced, thereby contributing to a reduction of the number of assemblingsteps.

The thin-film MI sensor 103 shown in FIG. 29 is designed in such amanner that in the thin-film MI element 103 a having the first electrode107 and the second electrode 108 disposed on both ends of the thin-filmmagnetic core 104 in the longitudinal direction, a third electrode 110is disposed at the middle point of the thin-film magnetic core 104, andthe bias thin-film coil 105 and the negative feedback thin-film coil 106(two bias thin-film coils 105 in total and two negative feedbackthin-film coils 106 in total) are formed on a portion of the thin-filmmagnetic core 104 between the first electrode 107 and the thirdelectrode 110 and formed on a portion of the thin-film magnetic core 104between the second electrode 108 and the third electrode 110 through theinsulating film 109, respectively. The bias thin-film coil 105 and thenegative feedback thin-film coil 106 are alternately wound on the sameplane at a given interval in the same direction and the same number ofturns, respectively. The thin-film Ml sensor 103 shown In FIG. 29 isstructured so as to extract the differential output from the firstelectrode 107 and the second electrode 108.

The thin-film MI sensor 103 shown in FIG. 30 is of the structure inwhich the earth terminals (five terminals in total, that is, the thirdelectrode 110, the right-side terminal of the bias thin-film coil 105 atthe left side of FIG. 30, the left-side terminal of the bias thin-filmcoil 105 at the right side of FIG. 30, the right-side terminal of thenegative feedback thin-film coil 106 at the left side of FIG. 30, theleft-side terminal of the negative feedback thin-film coil 106 at theright side of FIG. 30) are made common, as a result of which the numberof terminals connected to the sensor drive circuit is reduced, therebycontributing to a reduction of the number of assembling steps.

Two thin-film MI sensor 103 shown in FIG. 31 (two upper and lowersensors in FIG. 30) are disposed in parallel on the non-magneticsubstrate 70, and the respective thin-film magnetic cores 104 of theupper and lower thin-film MI elements 103 a of FIG. 31 are made up oftwo thin-film magnetic core elements 104 which are disposed in parallel.Those two thin-film magnetic cores 104 of the upper thin-film MIelements 103 a of FIG. 31 are electrically connected in series to eachother, and likewise, those two thin-film magnetic cores 104 of the lowerthin-film MI elements 103 a of FIG. 31 are electrically connected inseries to each other.

Subsequently, the characteristic of the thin-film MI sensor 103manufactured with the structure shown in FIG. 27 will be described. Inthis example, the dimensions of one thin-film magnetic core 104 are 20μm in width, 3 μm in thickness and 2000 μm in length as described above.Also, the bias thin-film coil 105 and the negative feedback thin-filmcoil 106 are alternately wound on the same surface as described above,and the number of turns is 42, respectively. With the structure in whichthe bias coil 105 and the negative feedback thin-film coil 106 arealternately wound around the thin-film magnetic core 104 on the samesurface, a bias magnetic field and a negative feedback magnetic fieldcan be uniformly applied to. the respective portions of the thin-filmmagnetic core 104, to thereby stabilize the characteristic as themagnetic sensor. The chip size of the entire element is 2.3 mm×1.6 mm,thus providing a very small-sized magnetic sensor.

FIG. 32 shows the magnetic field to impedance characteristic of onethin-film magnetic core 104 when the supply current is a sine wave of 20MHz and 20 mAp-p. As the applied magnetic field increases, the changerate ΔZ/Z0 of the impedance increases and becomes maximum at theanisotropy magnetic field Hk of the element, and further when Hex>Hk,Z/Z0 becomes smaller. Also, the change amount (magnetic fieldsensitivity) of the impedance per unit applied magnetic field becomesmaximum at about Hex=200 A/m and exhibits the magnetic field sensitivityof 0.4%/(A/m).

Subsequently, the drive principle of the differential drive typemagnetic sensor using two magnetic MI elements (for example, the abovethin-film MI elements 103 a) will be described in brief with referenceto FIGS. 33, 34 as well as FIG. 27. The differential drive type magneticsensor circuit uses two magnetic MI elements (thin-film MI elements 106a) having the bias thin-film coil 105 and the negative feedbackthin-film coil 106, and is made up of an oscillating circuit, adetecting circuit (diode bridge), an amplifying circuit and a negativefeedback resistor. When a high-frequency current is applied to twomagnetic MI elements (thin-film MI elements 103 a) by the oscillator toapply an external magnetic field to those elements, the impedance of theelements (thin-film MI elements 103 a and the thin-film magnetic core104) varies. Opposite bias magnetic fields are applied to those twomagnetic MI elements (thin-film MI elements 103 a), respectively. Forexample, if a positive bias magnetic field is applied to one of themagnetic MI elements (for example, the upper thin-film MI element 103 ain FIG. 1), a positive inclination is exhibited as shown in FIG. 33.Also, in this case, because a negative bias magnetic field is applied tothe other magnetic MI element (for example, the lower thin-film MIelements 103 a in FIG. 1), a negative inclination is exhibited as shownin FIG. 34. When those bias magnetic fields are detected anddifferentially detected by an operational amplifier, a change in theexternal magnetic field becomes a differential component. Therefore, theinclination of the magnetic sensor to which the outputs of two magneticMI elements (thin-film MI elements 103 a) are added appears, and achange in temperature of the magnetic MI elements (thin-film MI elements103 a) which is an in-phase component and so on can be removed.

The magnetic field detection magnetic sensor 81 is structured such thattwo thin-film MI elements shown in FIG. 27 are disposed so as to conductdifferential drive, and the circuit system of the above-describedmagnetic sensor is used as the differential drive circuit 80 shown inFIG. 25.

FIG. 35 shows a relation of the output voltage of the sensor (magneticfield detection magnetic sensor 81) to the applied magnetic field when anegative feedback with 240 A/m in bias coil magnetic field and 40% innegative feedback ratio is effected using the magnetic field detectionmagnetic sensor 81 having the above circuit structure. In this example,the supply current is of a pulse wave with 5 ns in pulse width, thepulse current is 35 mA and the amplification degree of the output is 25times.

The sensor characteristic exhibits excellent linearity within themeasured magnetic field of ±80 (A/m), the output exhibits the highoutput of 25 mV/(A/m), and the magnetic field resolution of 10⁻³ (A/m)is exhibited. Also, as shown in FIG. 36, the temperature characteristicof the sensitive cnaracteristic exhibits the excellent characteristic of0.1%/° C. Those results exhibit the excellent characteristic as thelinear magnetic field sensor.

Also, in case of the element using a negative feedback coil in which acopper wire is wound around an amorphous wire, in order to obtain thesame linearity as that of FIG. 35, a negative feedback of about 300%must be effected. The reason that the thin-film coils (bias thin-filmcoil 105 and negative feedback thin-film coil 106) have the samelinearity as that of the negative feedback coil where the copper wire iswound around the amorphous wire with the negative feedback ratio ofabout ⅙ is that the coils (bias thin-film coil 105 and negative feedbackthin-film coil 106) are allowed to approach the magnetic core (thin-filmMI magnetic core 104) with the result that the coil efficiency of thethin-film coils (the bias thin-film coil 105 and negative feedback coil106) is enhanced as described with reference to the bias coil.

Hereinbefore, although the embodiments of the present invention weredescribed, various modifications and applications can be made within thesubject of the present invention, and those modifications andapplications are not intended to be removed from the scope of thepresent invention.

As was described in detail above, according to the first to ninthaspects of the present invention, in the thin-film magnetic impedanceelement, the non-magnetic film is inserted into the middle of themagnetic film to provide two layers of magnetic thin-films, as a resultof which the magnetization vectors of the upper and lower magnetic filmsare coupled by the magnetrostatic coupling to keep them in a magneticclose state. With this state, the internal magnetization energy of thethin-film is minimized, and the thin-film having a two-layer structureis also structured by only 180° magnetic domain, whereby the Ml effectbecomes larger as compared with that of the single-layer film. For thosereasons, the high-sensitive magnetic impedance elements can be provided.

According to the tenth, eleventh, seventeenth and eighteenth aspects ofthe present invention, at least two thin-film magnetic cores aredisposed in parallel and the respective thin-film magnetic cores areelectrically connected in series to each other. Accordingly, because theimpedance of the magnetic impedance elements can be increased withoutIncreasing the chip size of the elements, the magnetic sensor small insize and high in output can be obtained.

The thin-film bias coil and the thin-film negative feedback coil areformed on the thin-film magnetic core via an insulator, thereby beingcapable of miniaturizing and mass-producing the magnetic impedanceelement. Also, because the thin-film coil manufactured with the abovestructure is high in coil efficiency, a required bias magnetic field isobtained with a small current, and the linearity of the output to themagnetic field can be improved with the small negative feedback amount.For those reasons, the thin-film linear magnetic field sensor which ishigh in sensitivity, excellent in the linearity of sensitivity andexcellent in the temperature characteristic can be provided. Inaddition, since the bias thin-film coil and the negative feedbackthin-film coil are alternately wound, the bias magnetic field and thenegative feedback magnetic field can be uniformly applied to therespective portions of the thin-film magnetic core, to thereby stabilizethe characteristic as the magnetic sensor.

According to the twelfth to eighteenth aspects of the present invention,the differential type magnetic sensor can be manufactured with theentire size miniaturized. For that reason, since a uniform magneticfield can be applied to two magnetic impedance elements on the samenon-magnetic substrate even when measuring a magnetic field occurring ina micro space, the uniform output can be differentially extracted fromthe respective magnetic impedance elements. In addition, as describedabove, the miniaturizing can lead to the improvement in mass production.

Further, in the above magnetic impedance element, with the structurewhere the respective one electrodes of the electrodes of the thin-filmmagnetic core, the electrodes of the thin-film bias thin-film coil andthe electrodes of the thin-film negative feedback thin-film coils can becommonly connected to each other, the portions connected to the externalcircuits are reduced in number. As a result, the magnetic sensor whichcan reduce the number of steps for connection to the sensor drivecircuit by means of the wire bonding or the like in a process ofmanufacturing the magnetic sensor and is high in reliability can beobtained.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and modifications and variations are possible in lightof the above teachings or may be acquired from practice of theinvention. The embodiments were chosen and described in order to explainthe principles of the invention and its practical application to enableone skilled in the art to utilize the invention in various embodimentsand with various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the claims appended hereto, and their equivalents.

What is claimed is:
 1. A magnetic impedance element including asubstrate made of a non-magnetic material and at least two thin-filmmagnetic cores formed on said substrate and having an electrode on afirst end of each of said thin-film magnetic cores characterized in thatsaid at least two thin-film magnetic cores are disposed in parallel andsaid respective thin-film magnetic cores are electrically connected inseries to each other by non-magnetic conductor at a second end of eachof said thin-film magnetic cores.
 2. A magnetic impedance element asclaimed in claim 1, wherein at least two of said thin-film magneticcores have in common a thin-film bias coil and a thin-film negativefeedback coil formed through an insulator, said thin-film bias coil andsaid thin-film negative feedback coil are alternately wound on a sameplane at a given interval in a same direction and a same number ofturns.